masking a video to show underlying still
I was using mix nodes to join the 2 layers. I order to do this you should use an Alpha Over node. My thanks to CGCookie for their posting on YouTube
https://www.youtube.com/watch?v=1eQst8SAVRE&amp;t=3s
it is version 2.8 but did the trick for me. An added bonus was the multiple masking technique they showed.
I can't add a picture at this point as when posting it seems I overwrite the text so I'll comment afterwards with the screenshot.
Many thanks.
Rob.